This invention generally relates to the field of fiber optic test and measurement, and more particular to an instrument for measuring optical spectra.
In general, optical spectra are measured using either a tunable filter or a spatially dispersing element where the deflection angle is a function of the wavelength. The dispersing element is in general a prism or a grating such that for each wavelength a certain angle of deflection is defined. Both possibilities require mechanical tuning of the element or a detector array for analyzing the optical spectrum.
Dispersion in optical materials can, as described above, be transformed into a wavelength dependent spatial intensity distribution. Another consequence of dispersion is a wavelength dependent distribution of the transmission times through the dispersive media, the so called chromatic dispersion.
Optical spectra can therefore also be measured by monitoring the time of flight of an optical pulse through the dispersive element. In order to provide sufficient chromatic dispersion the dispersive element has to be very long which seems to make the realization of an instrument of this kind impossible. On the other hand recent developments of optical fibers and fiber optical components open a way towards this approach of a temporal spectrometer.
The advantage of this kind of spectrometer is that it does not need any mechanical tuning and calibration and that it can be implemented in an “all fiber approach” i.e. the light never has to leave the optical fiber. This allows the easy implementation of this spectrometer into other instruments allowing e.g. the realization of a universal test instrument for chromatic dispersion, polarization mode dispersion (PMD) and spectral attenuation.